1. Field of the Invention
This invention relates generally to picture frames, and more particularly to means facilitating assembly of metal picture frames.
2. Description of the Prior Art
The prior art has disclosed various ways of assembling picture frames. Three patents of particular interest in this regard are U.S. Pat. No. 3,534,490 issued Oct. 20, 1970 to D. P. Herbert, U.S. Pat. No. 3,965,601 issued June 29, 1976, and U.S. Pat. No. 4,122,617 issued Oct. 31, 1978, both to Helmar Nielson. In the former of these patents, the frame members are metal extrusions and are held together at the corners by angled members having set screws threaded therein and bearing on portions of the frame members to lock the angle members in the frame members at the corners. In the Nielson patents, the frame members are also made of metal extrusions of a cross section similar to but slightly different from those in Herbert. In the Nielson construction, several different types of corner pieces are employed with set screws to hold the corners together.
Although the Herbert patent discloses one way of holding extrusions together at corners to form a picture frame, and the Nielson patents show another way to do the same thing and, at the same time, force the corners together at the front of the frame, both have some disadvantages. One primary disadvantage can be best recognized when one considers the fact that there is a significant market for non-professionals, who wish to do their own work in framing pictures. Occasionally such individuals do not get the corners together quite adequately. The Nielson patents represent an effort to improve the ability of an individual to make a good corner. But in one embodiment of Nielson, where the L-shaped bearing plate 28 is used, this involves an extra piece at each of the corners, thus increasing the expense, weight, and number of pieces the user must deal with at each corner. In the other embodiments, where only one piece is used, and in the Herbert construction, the set screw bears on the aluminum frame itself. If the corner is not properly assembled the first time, and the set screw is tightened in place, it will make it difficult to ever correctly assemble the corner thereafter. The reason for this is the fact that, once tightened, the set screw normally leaves a dent in the metal. At each subsequent reassembly of the corner, the set screw tends to re-seat itself in the dent made the first time.